e-window: hide unsensitive actions in webapp mode

https://bugzilla.gnome.org/show_bug.cgi?id=685216
ephy-about-handler: add content charset
ephy-window: disable new window creation in application mode

Also incognito windows.

https://bugzilla.gnome.org/show_bug.cgi?id=703929
Updated Russian translation
Set up build system for user help
Add es to the help/Makefile.am
Remove duplicate GtkBuilder property
Update links to help, add app menuitem

Update ephy_gui_help to link to pages, not sections. Update links to
pages in the new help. Add an app menu Help item. Change the link from
the preference dialog to link to the pref.page because one page per tab
is not compatible with the help style…
Add help buttons to the pdm and pref dialogs
Updated Spanish translation